Simplify the following expression: $z = \dfrac{8a + 9}{5} \div \dfrac{2a}{4}$
Explanation: Dividing by an expression is the same as multiplying by its inverse. $z = \dfrac{8a + 9}{5} \times \dfrac{4}{2a}$ When multiplying fractions, we multiply the numerators and the denominators. $z = \dfrac{ (8a + 9) \times 4 } { 5 \times 2a}$ $z = \dfrac{32a + 36}{10a}$ Simplify: $z = \dfrac{16a + 18}{5a}$